Dwell Time Control System And Method With Automatic Pressure Switch Point Adjustment

ABSTRACT

A dwell time control system and method for automatically adjusting the selection and timing of a sequence of pressures used to drive the plunger in a parison mold during the parison forming process. The timing of characteristics of the observed press curve from one or more previous parison forming cycles are ascertained and used to control the timing of the changes in pressure during a subsequent parison forming cycle. The timings of these changes of pressure are determined as predetermined percentages of the timings of the characteristics in order to prevent the blow mold from being forced open and in order to prevent the occurrence of an overpressed finish.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation of copending U.S. patentapplication Ser. No. 13/232,039, filed on Sep. 14, 2011, entitled “DwellTime Control Method and System With Automatic Pressure Switch PointAdjustment,” now U.S. Pat. No. 8,561,428, granted on Oct. 22, 2013,which is assigned to the assignee of the present patent application andwhich is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to the pressure used to operatethe plunger in a parison mold, and more particularly to a dwell timecontrol system and method for automatically adjusting the selection andtiming of a sequence of pressures used to drive the plunger during theparison forming process.

Glass containers are made in a manufacturing process that has threeparts, namely the batch house, the hot end, and the cold end. The batchhouse is where the raw materials for glass (typically including sand,soda ash, limestone, cullet (crushed, recycled glass), and other rawmaterials) are prepared and mixed into batches. The hot end begins witha furnace, in which the batched materials are melted into molten glass,and from which a stream of molten glass flows.

The molten glass is cut into cylinders of glass called gobs, which fallby gravity into blank molds, sometimes referred to as parison molds. Inthe blank molds, a pre-container referred to as a parison is formed,typically by using a metal plunger to push the glass into the blankmold, or alternately by blowing the glass from below into the blankmold. The parison is inverted and transferred to a mold, where it isblown out into the shape of the container. An annealing processperformed in an annealing oven or Lehr heats the containers and thenslowly and evenly cools them over an extended time period to preventthem from having weakened glass caused by stresses caused by unevencooling. The equipment at the cold end of the glass containermanufacturing process inspects the containers to ensure that they are ofacceptable quality.

The present invention is concerned with the parison formation processusing a plunger to push the glass into the blank mold. Parisons aremolded in a blank mold in an inverted position. The blank mold has twohalves, and completing the finish portion are two neck ring moldslocated below the blank mold halves, with an upwardly oriented plungerextending through the neck ring halves and into the bottom of the blankmold halves. The blank mold halves are open at the tops thereof, and agob of molten glass drops through this opening into the blank moldhalves. A baffle is placed on top of the blank mold halves to close theopening at the top thereof, and the plunger is raised to force the gobto fill the entire cavity defined by the blank mold halves, the neckring halves, and the baffle, thereby forming the parison. Uponcompletion of the cycle, the baffle is removed and the mold halves open,with the neck ring halves then transporting the parison to the blowmolds.

Plunger contact time or dwell time is a particularly important parameterwhen producing in a narrow neck press and blow glass containermanufacturing process or in a press and blow production in general. Thefull contact of the plunger with the glass in the gob that occurs duringplunger contact or dwell time influences the characteristics of parisonsproduced for use in further steps in the glass container formingprocess. While dwell time depends on a number of parameters includingfriction in the movement of the plunger and glass temperature, it canalso be strongly influenced by the pressure driving the plunger in itsupward motion.

The plunger was formerly driven by a hydraulic system, as shown forexample in U.S. Pat. No. 4,662,923, to Vajda et al. and U.S. Pat. No.4,867,778, to Pinkerton et al., both of which are assigned to theassignee of the present patent application, and both of which are herebyincorporated herein by reference in their entirety. Both of thesepatents used feedback to monitor the position of the plunger and to useplunger position information to control the parison formation process toimprove parison uniformity and quality.

In order to reduce the risk of fire associated with the use of hydraulicfluid in the operation of the plunger and other system components,pneumatic systems using compressed air were adopted, as illustrated inEuropean Patent No. 0691940, to Plater et al., and in U.S. Pat. No.5,800,590, to Pilskar, both of which are assigned to the assignee of thepresent patent application, and both of which are hereby incorporatedherein by reference in their entirety. The '940 Patent used aproportional control valve operated by a microcontroller dependent uponposition and pressure feedback signals from the plunger drive piston andcylinder. The '590 Patent used an initial higher pressure for a shorttime followed by a succeeding lower pressure that was approximately 70%of the initial higher pressure to operate the plunger.

The operation of the plunger was further refined by controlling themovement of the plunger, as illustrated in U.S. Pat. No. 6,050,172, toSchwegler et al., and in U.S. Pat. No. 7,290,406, to Anheyer, both ofwhich are assigned to the assignee of the present patent application,and both of which are hereby incorporated herein by reference in theirentirety. The '172 Patent controls the timing of valves providingcompressed air to both sides of a piston driving the plunger, and the'406 Patent provides a feedback control system for driving the plungerat desired speeds.

After comparing the determined value with the desired dwell time, pastclosed loop controller increased or decreased the pressure for drivingup the plunger until the resulting dwell time corresponds to the desireddwell time value has been achieved. However, simply increasing thepressure for plunger movement resulted in bottle defects, especiallyduring dwell time. An alternative solution was moving the plunger upwith different pressures (high, medium, low). However, this alternativepresented problems in selecting when to switch from a higher to a lowerpressure.

An illustration of such a problem is found in European Patent No.1466871, to Krumme, which is hereby incorporated herein by reference inits entirety, describes a method of operating the plunger that somewhatvaries the teachings of the '590 Patent to have second and thirddifferent lower pressures following an initial higher pressure tooperate the plunger. The second pressure is controlled to bring theplunger to completely fill the cavity defined by the mold halves, theneck ring halves, and the baffle at a fixed time at which point a fixedpressing time at the third pressure begins, which third pressure may beless than (in the primary embodiment) or greater than (in an alternateembodiment) the second pressure. Thus, the duration of the applicationsof the first and third pressures is predetermined (meaning that theduration of the second pressure is also predetermined since the overallmachine is operating at a predetermined speed), with the only variablebeing selecting the second pressure to be sufficient to completely fillthe cavity by the end of application of the second pressure.

A key deficiency of the '871 Patent is that the detection of the pointat which the plunger has completely filled the cavity is made bydetecting that the plunger has reached a predefined position rather thanactually detecting when the plunger has completely filled the cavity(see paragraph 0012 and Claim 2 of the '871 Patent). Measuring theposition of the plunger may be performed, for example, using the devicedisclosed in U.S. Pat. No. 6,185,829, to Geisel, which is herebyincorporated herein by reference in its entirety. Further, since thefirst pressure is only maintained for a short period of time, theoperation of the plunger with the second pressure must be sufficientlyhigh to reach the predefined position in the required time period, butnot so high that it will drive open the mold halves (see the lastsentence in paragraph 0010 of the '871 Patent). This is a compromisethat necessarily cannot result in optimizing system performance. Due tothe difficulties associated with multi-pressure pressing, most glasscontainer manufacturing plants still press with only a single pressurelevel that is sufficiently low to prevent the related defects, but alsocertainly less than an optimal solution.

It is accordingly desirable that the present invention provide animproved dwell time control method and system that results in theability to control the dwell time (the time that the plunger is in fullcontact with the parison). It is also desirable that the improved dwelltime control method and system automate the pressure switching processwithout requiring operator input once the process has been initiated. Itis further desirable that the dwell time control method and systemprevent the inadvertent opening of molds due to the occurrence ofoverpressure situations.

The dwell time control method and system of the present invention mustalso be of construction which is both durable and long lasting, and itshould also require little or no maintenance to be provided by the userthroughout its operating lifetime. In order to enhance the market appealof the dwell time control method and system of the present invention, itshould also be of inexpensive construction to thereby afford it thebroadest possible market. Finally, it is also an objective that all ofthe aforesaid advantages of the dwell time control method and system ofthe present invention be achievable without incurring any substantialrelative disadvantage.

The subject matter discussed in this background of the invention sectionshould not be assumed to be prior art merely as a result of its mentionin the background of the invention section.

Similarly, a problem mentioned in the background of the inventionsection or associated with the subject matter of the background of theinvention section should not be assumed to have been previouslyrecognized in the prior art. The subject matter in the background of theinvention section merely represents different approaches, which in andof themselves may also be inventions.

SUMMARY OF THE INVENTION

The disadvantages and limitations of the background art discussed aboveare overcome by the present invention. With this invention, theoperation of the plunger is controlled to optimize the dwell time of theplunger in contact with the parison. It results in the ability to fullyautomate the pressure switching process without requiring operator inputonce the process has been initiated. It also prevents the blank moldsfrom being inadvertently forced open due to the occurrence ofoverpressure situations in the operation of the plunger.

The dwell time control method and system of the present invention usesthree consecutive pressures to operate the plunger to form the parisonfrom the glass gob in the blank mold. The total time for operating theplunger to form the parison is predefined and unchangeable time periodsince it is established by the operational cycle timing of the I.S.machine, so the timings that are variable are the time that the pressureis changed from the first pressure to the second pressure, and the timethat the second pressure is changed to the third pressure. The dwelltime control method and system of the present invention bases thesetimes on the observed press curve from one or more previous parisonforming cycles.

The timing of two characteristics of the observed press curve from oneor more previous parison forming cycles are determined: the time atwhich the upper part of the mold becomes filled with glass from theglass gob that causes an increase in the resistance encountered by theparison is detected by the occurrence of a nonlinearity in the presscurve; and the time at which the mold becomes completely filled withglass from the glass gob that results in a slowing in the movement ofthe plunger below a particular level. By ascertaining these times (eachof which is measured from the initiation of the parison forming cycle),the times at which pressure changes can be determined.

The time that the pressure is changed from the first pressure to thesecond pressure is a first predetermined percentage of the ascertainedtime at which the upper part of the mold becomes filled with glass, andthe time that the pressure is changed from the second pressure to thethird pressure is a second predetermined percentage of the time at whichthe mold becomes completely filled with glass. The two characteristicsfrom one previous parison forming cycle may be used, or more than oneprevious parison forming cycles may be used by averaging the ascertainedtimes from the previous parison forming cycles. The first predeterminedpercentage is less than one hundred percent in order to prevent the blowmold from being forced open, and the second predetermined percentage isless than one hundred percent in order to prevent the occurrence of anoverpressed finish.

In a system embodiment for operating a plunger for molding a parison ina blank mold, the plunger being driven by a piston in a cylinder towhich a source of a pressurized medium may be applied at selectedpressures, the system includes: a position sensor that monitors theposition of the plunger in the blank mold versus time during at leastone parison forming cycle beginning at a time t₁ and ending at a timet₄; and a control system adapted to detect a first characteristic of themovement of the plunger at a time t₂ during the at least one monitoredparison forming cycle and a second characteristic of the movement of theplunger at a time t₃ in the at least one monitored parison formingcycle; wherein the control system is also adapted to determine a timet_(p2) before t₂ based on time t₂ and to determine a time t_(p3) beforet₃ based on time t₃; and wherein the control system is further adaptedto apply a first pressure from time t₁ to time t_(p2), a second pressurefrom time t_(p2) to time t_(p3), and a third pressure from time t_(p3)to time t₄ during a parison forming cycle subsequent to the at least onemonitored parison forming cycle, after a gob is loaded into the blankmold.

In a system embodiment for operating a plunger for molding a parison ina blank mold, the plunger being driven by a piston in a cylinder towhich a source of a pressurized medium may be applied at selectedpressures, the system includes: a position sensor that monitors theposition of the plunger in the blank mold versus time during a parisonforming cycle beginning at a time t₁ and ending at a time t₄; and acontrol system adapted to detect a nonlinearity in the movement of theplunger during the monitored parison forming cycle that is indicative ofan upper part of the blank mold having been filled with glass from theglass gob at a time t₂; wherein the control system is also adapted todetect a movement-related characteristic of the plunger during themonitored parison forming cycle that falls below a preselected level ata time t₃, the movement related characteristic falling below thepreselected level being indicative of the glass from the glass gobhaving been distributed throughout the blank mold to fill the blankmold; and wherein the control system is further adapted to apply a firstpressure from time t₁ to time t_(p2), a second pressure from time t_(p2)to time t_(p3), and a third pressure from time t_(p3) to time t₄ duringa parison forming cycle subsequent to the monitored parison formingcycle, after a gob is loaded into the blank mold; wherein the timeinterval between time t₁ and time t_(p2) is a first predeterminedpercentage of the time interval between time t₁ and time t₂; and whereinthe time interval between time t₁ and time t_(p3) is a secondpredetermined percentage of the time interval between time t₁ and timet₃.

In a system embodiment for operating a plunger for molding a parison ina blank mold, the plunger being driven by a piston in a cylinder towhich a source of a pressurized medium may be applied at selectedpressures, the system includes: a position sensor that monitors theposition of the plunger in the blank mold versus time during parisonforming cycles each beginning at a time t₁ and ending at a time t₄; anda control system adapted to detect a nonlinearity in the movement of theplunger during the monitored parison forming cycle that is indicative ofan upper part of the blank mold having been filled with glass from theglass gob at a time t₂; wherein the control system is also adapted todetect a movement-related characteristic of the plunger during themonitored parison forming cycle that falls below a preselected level ata time t₃, the movement related characteristic falling below thepreselected level being indicative of the glass from the glass gobhaving been distributed throughout the blank mold to fill the blankmold; and wherein the control system is further adapted to apply a firstpressure from time t₁ to time t_(p2), a second pressure from time t_(p2)to time t_(p3), and a third pressure from time t_(p3) to time t₄ duringa parison forming cycle subsequent to the monitored parison formingcycle, after a gob is loaded into the blank mold; wherein the timeinterval between time t₁ and time t_(p2) is a first predeterminedpercentage of the time interval between time t₁ and time t₂; and whereinthe time interval between time t₁ and time t_(p3) is a secondpredetermined percentage of the time interval between time t₁ and timet₃.

It may therefore be seen that the present invention teaches an improveddwell time control method and system that results in the ability tocontrol the dwell time (the time that the plunger is in full contactwith the parison). The improved dwell time control method and systemautomates the pressure switching process without requiring operatorinput once the process has been initiated. The dwell time control methodand system also prevents the inadvertent opening of molds due to theoccurrence of overpressure situations.

The dwell time control method and system of the present invention is ofa construction which is both durable and long lasting, and which willrequire little or no maintenance to be provided by the user throughoutits operating lifetime. The dwell time control method and system of thepresent invention is also of inexpensive construction to enhance itsmarket appeal and to thereby afford it the broadest possible market.Finally, all of the aforesaid advantages and objectives of the dwelltime control method and system of the present invention are achievedwithout incurring any substantial relative disadvantage.

DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention are best understoodwith reference to the drawings, in which:

FIG. 1 is a schematic cross-sectional view of a blank mold and anassociated plunger mechanism illustrating a glass gob in the blank moldwith the plunger in the loading position in the blank mold; and

FIG. 2 depicts two time-aligned plots associated with the dwell timecontrol method and system of the present invention, with the top plotshowing the pressure supplied to the plunger mechanism illustrated inFIG. 1 to press it into the glass gob to form a parison, and the bottomplot showing the actual position of the plunger in the blank mold.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Referring first to FIG. 1, a blank mold and an associated plungermechanism are illustrated. The mold includes two mold halves 30 and 32,which are shown as being closed atop two neck ring halves 34 and 36. Aplunger 38 is shown extending upwardly into the bottom of the moldhalves 30 and 32, with the plunger 28 being in the loading position inthe mold halves 30 and 32. A glass gob 40 is shown loaded into the moldhalves 30 and 32, with a baffle 42 shown atop the mold halves 30 and 32and closing the top ends thereof.

The plunger operating mechanism is housed by a lower cylinder 44, andupper cylinder 46 on top of the lower cylinder 44, and a cylinder cap 48that is mounted on top of the upper cylinder 46. A hollow sleeve 50 hasa cylindrical upper portion 52 that extends upwardly through thecylinder cap 48 and into the area between the bottom portions of theneck ring halves 34 and 36. The sleeve 50 has a central portion thatincludes an outwardly extending circular flange 54, and a bottom portion56. A guiding ring 58 is located at the top of the upper portion 52 ofthe sleeve 50, and the plunger 38 extends through the upper portion 52of the sleeve 50 and the guiding ring 58 and into the bottom of the moldhalves 30 and 32.

The bottom of the plunger 38 is mounted onto the top of a plunger base60, which is slidably mounted in the interior of the sleeve 50. Thebottom of the upper cylinder 46 has a reduced diameter aperture locatedtherein in which a piston rod 62 is slidably mounted. The piston rod 62is connected at its top end thereof to the bottom of the plunger base60, and at its bottom end to the top of a piston 64 that is slidablymounted in the bottom cylinder 44. It will be appreciated that movementof the piston 64 in the lower cylinder 44 will drive the plunger 38.

A cooling tube 66 extends from the closed bottom of the lower cylinder44 upwardly through the piston 64 and into the hollow interior of thepiston rod 64 to provide cooling fluid thereinto. A spring 68 is mountedin the upper cylinder 46, and extends between the top side of the bottomof the upper cylinder 46 and the bottom side of the circular flange 54.The spring 68 functions to bias the plunger 38 to its loading positionas shown in FIG. 1 by driving the circular flange 54 of the sleeve 50into contact with the underside of the cylinder cap 48 in the absence ofany downward pressure on the piston 64 in the lower cylinder 44.

Pressurized fluid (typically compressed air) may be supplied to drivethe piston 64 and the plunger upwardly through a first or lower inlet70, and pressurized fluid may be supplied to drive the piston 64 and theplunger 38 downwardly through a second or upper inlet 72. It should benoted that in order to drive the plunger 38 downwardly from the loadingposition it is illustrated in FIG. 1 it is necessary to overcome theforce of the spring 68. This will also cause the sleeve 50 and theguiding ring 58 to be lowered from their respective positionsillustrated in FIG. 1 to somewhat retract them from the neck ring halves34 and 36.

Pressurized fluid is supplied from a first pressure source 74 with boththe flow of pressurized fluid from the first pressure source 74 and thepressure at which the pressurized fluid is supplied to the lower inlet70 being controlled by a first proportional valve 76. Similarly,pressurized fluid is supplied from a second pressure source 78 with boththe flow of pressurized fluid from the second pressure source 78 and thepressure at which the pressurized fluid is supplied to the upper inlet72 being controlled by a second proportional valve 80 (although a simpleon/off valve will also suffice since the function is simply to drive thepiston 64 to retract the plunger downwardly).

The operation of the first proportional valve 76 and the secondproportional valve 80 are controlled by a control system 82, whichstores programmed information and data in a memory 84. The operation ofthe control system 82 may be monitored on a display 86, and controlledusing an input control 88. Information regarding the position of theplunger 38 is provided by a position sensor 90 that monitors theposition of the piston rod 62, the movement of which corresponds withthe position of the distal end of the plunger 38 in the mold halves 30and 32. The position sensor 90 uses the relative positions of the piston64 and the piston rod 62 with respect to the cooling tube 66 to providean input regarding the position of the plunger 38 to the control system82.

Referring next to FIG. 2, an exemplary use of a three-pressure operationto drive the plunger 38 (shown in FIG. 1) from the loading position (inwhich it is illustrated in FIG. 1) to form the parison from the glassgob in the blank mold is illustrated. According to the teachings of thepresent invention, the three consecutive pressures, referred to hereinas p1, p2, and p3, are cumulatively applied during a time periodbeginning at time t₁ and ending at time t₄. It will be appreciated bythose skilled in the art that a single cycle of the blow molding processlasts for a predefined and unchangeable time period that is determinedby the operational speed of the I.S. machine (typically one full cyclelasts for approximately four to five seconds). Similarly, the timeperiod beginning at time t₁ and ending at time t₄ is a predefined andsimilarly unchangeable time period that is established by the timing ofthe cycle of the operations of the I.S. machine (typically this timeperiod is approximately one second).

The dwell time control method and system of the present inventiondetects two events that occur during the time period that begins at timet₁ and ends at time t₄, with the respective times at which these twoevents occur being time t₂ and time t₃. The first of these events, whichoccurs at time t₂, is when the plunger 38 (shown in FIG. 1) has forcedthe glass gob 40 (also shown in FIG. 1) to hit the baffle 42 (also shownin FIG. 1), at which point a non-linear increase in resistance tofurther movement of the plunger 38 due to the upper part of the moldhaving been filled with glass from the glass gob 40.

This may be seen in FIG. 2 in the bottom plot which shows the positionof the plunger 38 in the blank mold at the point identified by theintersection of the plot with the time t₂. At the point where the upperpart of the mold is completely filled with glass from the glass gob 40,there is a readily observable nonlinear characteristic or “knee” in theplot of the position of the plunger 38 in the blank mold. This time t₂may be detected by the dwell time control method and system of thepresent invention by monitoring the first and second derivatives(velocity and acceleration) of the position of the plunger 38 in theblank mold.

The second of these events, which occurs at time t₃, is when the firstand second derivatives (velocity and acceleration) of the plunger 38have fallen below preset levels, which generally occurs when the glassfrom the glass gob 40 has been distributed throughout the entire blankmold, completely filling it. This may be seen in FIG. 2 in the bottomplot showing the position of the plunger 38 in the blank mold at thepoint identified by the intersection of the plot with the time t₃. Thetime period from time t₁ to time t₃ is parison forming time and is alsoreferred to as the “pressing time.” During the time period beginning attime t₃ and ending at time t₄, the final pressing of the glass in themold into a parison occurs. This time period, which is commonly referredto as the “dwell time,” is generally at least a certain time period, forexample approximately between 400 and 600 milliseconds.

Thus, what can be varied by the dwell time control method and system ofthe present invention are the time at which the first pressure p1 ischanged to the second pressure p2, which time will be referred to hereinas time t_(p2), and the time at which the second pressure p2 is changedto the third pressure p3, which time will be referred to herein as timet_(p3). The present invention uses the measured times t₂ and t₃ of twodetected events from the plot of the position of the plunger 38 in theblank mold during previous cycles as the triggering events to calculatethe time t_(p2) at which the pressure applied to the plunger 38 willchange from p1 to p2, and the time t_(p3) at which the pressure appliedto the plunger 38 will change from p2 to p3.

The first pressure p1 is highest since higher pressure is needed toovercome initial friction and to accelerate the movement of the plunger38. However, this higher first pressure p1 must be removed before theglass in the glass gob 40 hits the baffle 42 in order to prevent theblow mold from being forced open. In order to ensure that this does nothappen, the time interval between time t₁ and time t_(p2) after whichthe pressure applied to the plunger 38 will change from p1 to p2 isselected to be a percentage of the measured time interval between timet₁ and time t₂ for one or more previous I.S. machine cycles (if thistime interval is measured for more than one machine cycle, the measuredtimes may be averaged).

In a preferred embodiment, the time interval between time t₁ and timet_(p2) can vary from approximately sixty percent to approximatelyninety-five percent of the time interval between time t₁ and time t₂. Ina more preferred embodiment, the time interval between time t₁ and timet_(p2) can vary from approximately seventy percent to approximatelyninety percent of the time interval between time t₁ and time t₂. In amost preferred embodiment, the time interval between time t₁ and timet_(p2) is approximately eighty percent of the time interval between timet₁ and time t₂.

The number of prior cycles over which the time interval between time t₁and time t₂ can be measured and averaged may be varied from one cycle(in which case no averaging is needed) to one hundred cycles or evenmore in preferred embodiments, with consideration being given to abalancing of only recent cycles being used and a greater number ofcycles being used. In a more preferred embodiment, this balancing uses anumber of cycles that is between approximately three cycles andapproximately twenty cycles to calculate the average, and in a mostpreferred embodiment, this balancing uses approximately eight cycles tocalculate the average. In each case, the measurements of the timeinterval between time t₁ and time t₂ are used for the given number ofimmediately preceding cycles, so that a new average value is calculatedfor each succeeding cycle.

The third pressure p3 may be lower than the second pressure p2 in orderto have a higher pressure p2 to complete the pressing time of the glassgob 40 in the blank mold quickly and to have a lower pressure p3 inorder to prevent the occurrence of an overpressed finish. In this case,this higher second pressure p2 should be removed before the glass in theglass gob 40 fills the blank mold in order to prevent the finish frombeing overpressed. In order to ensure that this does not happen, thetime interval between time t₁ and time t_(p3) after which the pressureapplied to the plunger 38 will change from p2 to a lower p3 is selectedto be a percentage of the measured time interval between time t₁ andtime t₃ (alternately, it could instead be a percentage of the measuredtime interval between time t_(p2) and time t₃, or even a percentage ofthe measured time interval between time t₂ and time t₃, although thesealternatives are not the most preferred implementation of the dwell timecontrol method and system of the present invention).

In a preferred embodiment, the time interval between time t₁ and timet_(p3) can vary from approximately fifty percent to approximately ninetypercent of the time interval between time t₁ and time t₃. In a morepreferred embodiment, the time interval between time t₁ and time t_(p3)can vary from approximately sixty percent to approximately eightypercent of the time interval between time t₁ and time t₃. In a mostpreferred embodiment, the time interval between time t₁ and time t_(p3)is approximately seventy percent of the time interval between t₁ and t₃.

The number of prior cycles over which the time interval between time t₁and time t₃ can be measured and averaged may be varied from one cycle(in which case no averaging is needed) to one hundred cycles or evenmore in preferred embodiments, with consideration being given to abalancing of only recent cycles being used and a greater number ofcycles being used. In a more preferred embodiment, this balancing uses anumber of cycles that is between approximately three cycles andapproximately twenty cycles to calculate the average, and in a mostpreferred embodiment, this balancing uses approximately eight cycles tocalculate the average. In each case, the measurements of the timeinterval between time t₁ and time t₃ are used for the given number ofimmediately preceding cycles, so that a new average value is calculatedfor each succeeding cycle.

If the first alternate embodiment mentioned above is used instead, thetime interval between time t_(p2) and time t_(p3) can vary fromapproximately forty-five percent to approximately eighty-five percent ofthe time interval between time t_(p2) and time t₃. In a more preferredembodiment, the time interval between time t_(p2) and time t_(p3) canvary from approximately fifty-five percent to approximately seventy-fivepercent of the time interval between time t_(p2) and time t₃. In a mostpreferred embodiment, the time interval between time t_(p2) and timet_(p3) is approximately sixty-five percent of the time interval betweentime t_(p2) and time t₃.

In some instances (such as, for example, producing wide mouth glasscontainers) it may be desirable to have p3 be greater than p2 (and alsoto have p2 be greater than p1). This may be done because during thedwell time the plunger 38 is in contact with the parison in the glassgob 40 in the blank mold, and as such is either not moving or moving atsuch an exceedingly low rate that it has essentially no momentum. Assuch, it may be possible for the dwell time pressure to be higher thanthe second pressure p2 used during the pressing time, although thisalternatives is generally not the most preferred implementation of thedwell time control method and system of the present invention (exceptperhaps in the production of wide mouth glass containers).

Since the time period that begins at time t₁ and ends at time t₄ isfixed, and since it is desirable to have a dwell time beginning at timet₃ and ending at time t₄ that is at least a minimum time period long,such as, for example, between approximately 400 and 600 millisecondslong, it is possible in an alternate embodiment to have the objective ofdefining a desired value for the time t₃. By varying the values ofeither the second pressure p2 only, or by varying the values of both thefirst pressure p1 and the second pressure p2 with them in a fixedrelationship (e.g., the first pressure p1 is equal to 1.12 times thesecond pressure p2), this objective for a dwell time beginning at adesired value for the time t₃ can be realized in relatively few parisonforming cycles.

Depending upon the specific mold design, various loading possibilities,and the variations possible in other parameters, virtually everypossible combination of p1, p2, p3 levels could, in some instances, makesense. All possible combinations are thus viewed as being encompassed bythe improved dwell time control method and system.

It may therefore be appreciated from the above detailed description ofthe preferred embodiment of the present invention that it teaches animproved dwell time control method and system that results in theability to control the dwell time (the time that the plunger is in fullcontact with the parison in the gob). The improved dwell time controlmethod and system automates the pressure switching process withoutrequiring operator input once the process has been initiated. The dwelltime control method and system also prevents the inadvertent opening ofmolds due to the occurrence of overpressure situations.

The dwell time control method and system of the present invention is ofa construction which is both durable and long lasting, and which willrequire little or no maintenance to be provided by the user throughoutits operating lifetime. The dwell time control method and system of thepresent invention is also of inexpensive construction to enhance itsmarket appeal and to thereby afford it the broadest possible market.Finally, all of the aforesaid advantages and objectives of the dwelltime control method and system of the present invention are achievedwithout incurring any substantial relative disadvantage.

Although the foregoing description of the dwell time control method andsystem of the present invention has been shown and described withreference to particular embodiments and applications thereof, it hasbeen presented for purposes of illustration and description and is notintended to be exhaustive or to limit the invention to the particularembodiments and applications disclosed. It will be apparent to thosehaving ordinary skill in the art that a number of changes,modifications, variations, or alterations to the invention as describedherein may be made, none of which depart from the spirit or scope of thepresent invention. The particular embodiments and applications werechosen and described to provide the best illustration of the principlesof the invention and its practical application to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such changes, modifications,variations, and alterations should therefore be seen as being within thescope of the present invention as determined by the appended claims wheninterpreted in accordance with the breadth to which they are fairly,legally, and equitably entitled.

While the current application recites particular combinations offeatures in the claims appended hereto, various embodiments of theinvention relate to any combination of any of the features describedherein whether or not such combination is currently claimed, and anysuch combination of features may be claimed in this or futureapplications. Any of the features, elements, or components of any of theexemplary embodiments discussed above may be claimed alone or incombination with any of the features, elements, or components of any ofthe other embodiments discussed above.

What is claimed is:
 1. A system for operating a plunger for molding aparison in a blank mold, the plunger being driven by a piston in acylinder to which a source of a pressurized medium may be applied atselected pressures, the system comprising: a position sensor thatmonitors the position of the plunger in the blank mold versus timeduring at least one parison forming cycle beginning at a time t₁ andending at a time t₄; and a control system adapted to detect a firstcharacteristic of the movement of the plunger at a time t₂ during the atleast one monitored parison forming cycle and a second characteristic ofthe movement of the plunger at a time t₃ in the at least one monitoredparison forming cycle; wherein the control system is also adapted todetermine a time t_(p2) before t₂ based on time t₂ and to determine atime t_(p3) before t₃ based on time t₃; and wherein the control systemis further adapted to apply a first pressure from time t₁ to timet_(p2), a second pressure from time t_(p2) to time t_(p3), and a thirdpressure from time t_(p3) to time t₄ during a parison forming cyclesubsequent to the at least one monitored parison forming cycle, after agob is loaded into the blank mold.
 2. A system as defined in claim 1,wherein the first characteristic of the movement of the plunger detectedby the control system comprises: a nonlinearity detected by the controlsystem in the movement of the plunger with respect to time which isindicative of an upper part of the mold having been filled with glassfrom the glass gob.
 3. A system as defined in claim 1, wherein the firstcharacteristic of the movement of the plunger detected by the controlsystem at the time t₂ is the upper part of the mold having been filledwith glass from the glass gob.
 4. A system as defined in claim 1,wherein the second characteristic of the movement of the plungerdetected by the control system comprises: a movement-relatedcharacteristic of the plunger detected by the control system that fallsbelow a preselected level which is indicative of the glass from theglass gob having been distributed throughout the entire blank mold tocompletely fill it.
 5. A system as defined in claim 1, wherein thesecond characteristic of the movement of the plunger detected by thecontrol system at time t₃ is the glass from the glass gob having beendistributed throughout the entire blank mold to completely fill it.
 6. Asystem as defined in claim 1, wherein the first pressure is larger thaneither the second pressure or the third pressure.
 7. A system as definedin claim 6, wherein the second pressure is greater than the thirdpressure.
 8. A system as defined in claim 6, wherein the third pressureis greater than the second pressure.
 9. A system as defined in claim 1,wherein the position sensor monitors the position of the plunger in theblank mold versus time during each parison forming cycle beginning at atime t₁ and ending at a time t₄.
 10. A system as defined in claim 9,wherein the control system is adapted to further detects the point intime during more than one monitored parison forming cycle at which themovement of the plunger in the blank mold with respect to time exhibitsa non-linearity that is indicative of an increase in resistance tofurther movement of the plunger, that point in time being the time t₂;and wherein the control system is adapted to further detect the point intime during more than one monitored parison forming cycle at which themovement of the plunger in the blank mold with respect to time fallsbelow a minimum threshold indicative of the end of a pressing cycle,that point in time being the time t₃.
 11. A system as defined in claim10, wherein the control system further averages the times t₂ during themore than one monitored parison forming cycle to determine the time t₂for the parison forming cycle subsequent to the more than one monitoredparison forming cycles.
 12. A system as defined in claim 11, wherein themore than one monitored parison forming cycles include approximatelyeight monitored parison forming cycles.
 13. A system as defined in claim10, wherein the control system further averages the times t₃ during themore than one monitored parison forming cycle to determine the time t₃for the parison forming cycle subsequent to the more than monitoredparison forming cycles.
 14. A system as defined in claim 13, wherein themore than one monitored parison forming cycles include approximatelyeight monitored parison forming cycles.
 15. A system as defined in claim1, wherein the time interval between time t₁ and time t_(p2) iscalculated by the control system to be a first predetermined percentageof a time interval based upon the time interval between time t₁ and timet₂ for the at least one monitored parison forming cycle; and wherein thetime interval between time t₁ and time t_(p3) is calculated by thecontrol system to be a second predetermined percentage of a timeinterval based upon the time interval between time t₁ and time t₃ forthe at least one monitored parison forming cycle.
 16. A system asdefined in claim 15, wherein the first predetermined percentagecomprises approximately eighty percent.
 17. A system as defined in claim15, wherein the second predetermined percentage comprises approximatelyseventy percent.
 18. A system as defined in claim 1, wherein the controlsystem is adapted to adjust either the second pressure or both the firstpressure and the second pressure to achieve a desired dwell timeinterval between the time t₃ and the time t₄.
 19. A system for operatinga plunger in a blank mold to mold a parison from a glass gob, theplunger being driven by a piston in a cylinder to which a source of apressurized medium may be applied at selected pressures, the systemcomprising: a position sensor that monitors the position of the plungerin the blank mold versus time during a parison forming cycle beginningat a time t₁ and ending at a time t₄; and a control system adapted todetect a nonlinearity in the movement of the plunger during themonitored parison forming cycle that is indicative of an upper part ofthe blank mold having been filled with glass from the glass gob at atime t₂; wherein the control system is also adapted to detect amovement-related characteristic of the plunger during the monitoredparison forming cycle that falls below a preselected level at a time t₃,the movement related characteristic falling below the preselected levelbeing indicative of the glass from the glass gob having been distributedthroughout the blank mold to fill the blank mold; and wherein thecontrol system is further adapted to apply a first pressure from time t₁to time t_(p2), a second pressure from time t_(p2) to time t_(p3), and athird pressure from time t_(p3) to time t₄ during a parison formingcycle subsequent to the monitored parison forming cycle, after a gob isloaded into the blank mold; wherein the time interval between time t₁and time t_(p2) is a first predetermined percentage of the time intervalbetween time t₁ and time t₂; and wherein the time interval between timet₁ and time t_(p3) is a second predetermined percentage of the timeinterval between time t₁ and time t₃.
 20. A system for operating aplunger in a blank mold to mold a parison from a glass gob, the plungerbeing driven by a piston in a cylinder to which a source of apressurized medium may be applied at selected pressures, the systemcomprising: a position sensor that monitors the position of the plungerin the blank mold versus time during parison forming cycles eachbeginning at a time t₁ and ending at a time t₄; and a control systemadapted to determine a time t₂ in each monitored parison forming cycleat which an upper part of the mold has been filled with glass from theglass gob; wherein the control system is also adapted to determine atime t₃ in each monitored parison forming cycle at which the glass fromthe glass gob has been distributed throughout the entire blank mold tocompletely fill it; and wherein the control system is further adapted toapply a first pressure from time t₁ to time t_(p2), a second pressurefrom time t_(p2) to time t_(p3), and a third pressure from time t_(p3)to time t₄ during each parison forming cycle, after a gob is loaded intothe blank mold; wherein the time interval between time t₁ and timet_(p2) is a first predetermined percentage of a time interval based uponthe time interval between time t₁ and time t₂ for one or more previousparison forming cycles; and wherein the time interval between time t₁and time t_(p3) is a second predetermined percentage of a time intervalbased upon the time interval between time t₁ and time t₃ for one or moreprevious parison forming cycles.